Nitric oxides (NOx), mainly consisting of nitric oxide (NO) and nitrogen dioxide (NO2), are relatively toxic pollutants formed during a combustion processes. Such pollutants may be present in exhaust gases discharged from gas engines, gas turbines in aircraft, diesel engines and in power generation. Increasing concerns over air quality and new regulations have forced, and will continue to force the installation of NOx emissions control systems.
Selective noncatalytic reduction (SNCR) technology is one of the technologies that has been used for NOx removal, in which a reducing agent, usually ammonia (or urea) is added to the combustion gas stream. The ammonia reduces NO molecules present according to the reaction:6NH3+4NO→5N2+10H2O
However, the current SNCR efficiency is reportedly around 30-60% which is much lower than that of Selective Catalytic Reduction (SCR) technology. While SNCR technology does not rely upon a catalyst, its relatively low conversion makes it difficult to achieve economic competitiveness versus SCR technology, which operates at relatively lower temperature with the assistance of a catalyst.